President Trump had wished Flynn "good luck" on Twitter earlier Tuesday, adding it "will be interesting to see what he has to say."

Former national security adviser Michael Flynn arrives for his sentencing hearing at U.S. District Court in Washington on Dec. 18, 2018.Jonathan Ernst / Reuters

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Dec. 18, 2018, 12:05 PM GMT / Updated Dec. 18, 2018, 12:54 PM GMT

By Allan Smith

A federal judge, in a dramatic hearing on Tuesday, agreed to delay the sentencing hearing for former national security adviser Michael Flynn because he may be able to provide additional cooperation to federal investigators, and get credit for it.

Flynn was due to be sentenced for lying to the FBI last year about his contacts with Russian officials in the aftermath of the 2016 campaign as part of special counsel Robert Mueller's investigation into Russian election interference.

But during Tuesday's hearing, U.S. District Judge Emmet Sullivan pulled few punches when it came to Flynn's conduct, saying he couldn't hide his "disgust" with the retired Army lieutenant general and questioned why he hadn't been charged with treason.

"Arguably, you sold your country out" by working as an unregistered foreign agent, Sullivan told Flynn, a reference to Flynn's admitted lobbying work on behalf of the Turkish government.

After a recess, Sullivan walked back some of his stronger remarks. The judge said he "may have misspoken," because he asserted that Flynn served as an unregistered foreign agent while he was working in the White House as national security adviser. That lobbying work was conducted while Flynn was acting as an adviser to Donald Trump's presidential campaign, though it ended prior to Trump taking office.

Still, Sullivan said he couldn't guarantee Flynn wouldn't get prison time if the hearing proceeded as scheduled.

"If you want to postpone this, and come back at some later point...that's fine with me," Sullivan said after special counsel Robert Mueller's prosecutors raised the possibility that Flynn had more to offer.

Flynn's lawyers took the judge's suggestion, requesting — and receiving — a postponement. His defense explained that there was a possibility that Flynn may be asked to testify in a case involving his business associates.

Two of Flynn's former associates were charged on Monday with conspiracy to act as agents of a foreign government for "covertly and unlawfully" trying to influence American politicians in a plot to extradite a Turkish cleric living in the U.S. That case was filed in the Eastern District of Virginia.

"We wish General Flynn well," White House Press Secretary Sarah Sanders said on Tuesday, in response to questions about the delay in his case.

Since pleading guilty to lying to the FBI last year, Flynn has cooperated with the special counsel, who examining whether the Trump campaign colluded with Russian officials as part of the broader election interference investigation. Mueller's prosecutors wrote in a sentencing memo to the judge last week that Flynn provided his team with "substantial assistance," adding that he should receive little to no prison time.

Sullivan appeared to disagree, also seeming to take issue with the sentencing memo filed by Flynn's attorneys, which suggested that FBI agents may have acted improperly in their interview of Flynn and entrapped him into lying.

Under direct questioning from the judge, Flynn said he would not change his guilty plea nor challenge the circumstances under which he was interviewed.

“I was aware” that lying to the FBI was a crime, Flynn told Sullivan, adding that he accepted responsibility for his false statements.

"This is a very serious offense," Sullivan said. "A high ranking senior official of the government making false statements to the federal bureau of investigation while in the White House."

Before court convened, President Donald Trump wished Flynn "good luck," adding that he was interested in hearing what Flynn said in court.

Good luck today in court to General Michael Flynn. Will be interesting to see what he has to say, despite tremendous pressure being put on him, about Russian Collusion in our great and, obviously, highly successful political campaign. There was no Collusion!

During Tuesday's press briefing, White House press secretary Sarah Sanders was asked what the difference was between Trump's former longtime lawyer Michael Cohen, whom the president has called a "rat," and Flynn. Both Cohen, who was sentenced to three years in prison earlier this month after pleading guilty to nine federal charges of tax evasion, violating campaign finance laws, and lying to banks and to Congress, and Flynn are cooperating with federal investigators.

"Look, we know Michael Cohen to be a liar on a number of fronts and the president's opinion is extremely clear on that front," Sanders said. "I don't see any reason to go beyond that comment at this point."

Claiming that the FBI "ambushed" Flynn, Sanders also insisted that Flynn's lies had nothing to do with Trump.

Rep. Adam Schiff, the California Democrat who is likely to become the House Intelligence Committee chairman when the new Congress convenes in January, tweeted after the hearing that Flynn should come before his committee to testify.

After the judge acknowledged the seriousness of Flynn’s conduct, he has allowed Trump’s former National Security Advisor to defer sentencing until after he has fully cooperated with the government.

It will be important that Flynn also cooperate with our Committee and testify.

That discussion, as the notes showed, centered around Flynn's conversations with the then-Russian ambassador to the U.S., Sergey Kislyak, during the transition period after the 2016 election. Specifically, Flynn was asked at length about whether he discussed with Kislyak a UN vote on Israeli settlements the Obama administration abstained from and the sanctions placed on Russia in response to alleged election interference just prior to Trump taking office.

Flynn said he had a closed-door meeting with Kislyak following the election, but the details on that are redacted. Flynn said the purpose of his frequent communication with Kislyak, whom he exchanged multiple phone calls and text messages with during the transition, was to improve ties with Russia so the two nations could better fight terrorism together.

Sullivan ordered the document be made public after Flynn's attorneys made the suggestion in their sentencing memo of possible untoward conduct by the FBI agents in that interview.